D-Dimer FEU to DDU Converter
D-Dimer FEU to DDU Converter
Convert D-dimer between fibrinogen equivalent units and D-dimer units — two incompatible reporting systems that, confused, either miss a pulmonary embolism or trigger an unnecessary CT scan.
D-Dimer FEU to DDU Converter
FEU → DDU, ÷2D-dimer 620 µg/L FEU
Formula
- FEU
- fibrinogen equivalent units — the assay reports the mass of fibrinogen-equivalent material detected
- DDU
- D-dimer units — the assay reports the mass of the D-dimer fragment itself
- ÷ 2
- a nominal conversion, not an exact molecular one — see below
Worked example
D-dimer 620 µg/L FEU
620 ÷ 2 = 310 µg/L DDU
310 is above the conventional 250 µg/L DDU cut-off — a raised result
Common cut-offs and unit equivalence
| System | Conventional cut-off | Equivalent |
|---|---|---|
| FEU | 500 µg/L | = 1000 DDU-equivalent ng/mL is NOT the same — see note |
| DDU | 250 µg/L | = 500 µg/L FEU |
| µg/L | — | = ng/mL (same magnitude) |
| mg/L | — | = µg/mL (same magnitude) |
Why the same D-dimer result can look normal or abnormal
D-dimer is reported in two incompatible unit systems, and this is one of the more consequential sources of laboratory confusion in acute medicine. Fibrinogen equivalent units (FEU) report the mass of material detected as if it were fibrinogen, the parent molecule the assay was originally calibrated against; D-dimer units (DDU) report the mass of the D-dimer fragment itself. Because fibrinogen has roughly twice the molecular mass of the D-dimer fragment it breaks down into, an FEU result is approximately twice the equivalent DDU result for identical plasma.
The conventional cut-offs follow that ratio: 500 µg/L FEU and 250 µg/L DDU are meant to represent the same clinical threshold. Applying an FEU cut-off to a DDU result — or the reverse — moves the threshold by a factor of two in the wrong direction. Used one way it misses pulmonary emboli that should have gone to imaging; used the other way it sends patients for unnecessary CT pulmonary angiography and its associated radiation and contrast risk.
Two further notes worth keeping in mind: µg/L is numerically the same as ng/mL, and mg/L the same as µg/mL, so those pairs need no conversion. And the factor of two here is a nominal, population-level conversion rather than an exact molecular equivalence — individual assay platforms are not perfectly interchangeable, so a patient being followed serially should stay on one assay and one unit system throughout.
Frequently asked questions
Is FEU or DDU the bigger number?
FEU. Fibrinogen equivalent units report a value roughly twice the D-dimer units result for the same plasma, because fibrinogen has about twice the molecular mass of the D-dimer fragment the assay is really detecting.
What is the D-dimer cut-off for excluding PE or DVT?
Conventionally 500 µg/L FEU or 250 µg/L DDU — the same clinical threshold expressed in each system. Always confirm which unit your laboratory report and your clinical pathway use before applying a cut-off.
Is µg/L the same as ng/mL?
Yes, they are numerically identical, as are mg/L and µg/mL. No conversion factor is needed between those pairs — only between FEU and DDU.
Why does this conversion matter clinically?
Applying the wrong unit’s cut-off to a result reported in the other system shifts the threshold by roughly a factor of two, which can either miss a venous thromboembolism or trigger an unnecessary CT scan.
Related calculators
References
- Righini M, Perrier A, De Moerloose P, Bounameaux H. D-dimer for venous thromboembolism diagnosis: 20 years later. J Thromb Haemost. 2008;6(7):1059–71.
- Olson JD. D-dimer: an overview of hemostasis and fibrinolysis, assays, and clinical applications. Adv Clin Chem. 2015;69:1–46.